The present invention relates to a bearing seal having one end fit in a seal groove formed in the inner peripheral edge of an outer race, and the other end extending toward a groove formed in the outer peripheral edge of an inner race, and in particular, to a seal suitable for a prelubricated rolling bearing with a non-rotable inner race and a rotatable outer race.
An electromagnetic clutch used in an air conditioner or a super charger for vehicles typically employs a rolling bearing of the type which includes a non-rotatable inner race and a rotatable outer race. Recently, such a rolling bearing has been used under severe operating conditions, e.g., at high temperature and particularly in applications where it is required to rotate at high speeds. While the bearing is being rotated at a high speed, grease may leak from the bearing, or grease may vaporize at high temperature. The grease in vapor form leaks from a seal lip and is then scattered directly over a clutch disk. This results in slippage of the clutch disk.
FIG. 5 shows a prior art electromagnetic clutch for use in a supercharger. In FIG. 5, a rolling bearing B' includes balls in rows and engages the inner surface 16 of a clutch disk A. The bearing has an outer race with which a grease catcher C is contacted. As shown in FIG. 6, which is an enlarged partial view of the rolling bearing B' a circular reinforcing core 10a is, for example, used to reinforce a resilient seal 1a. The resilient seal 1a extends between a seal groove 3 formed in the inner peripheral edge of an outer race 2 and a corresponding groove 5 formed in an inner race 4. The resilient seal 1a has an inner lip 9a axially extending toward an inner wall 8 of the groove 5 and a center lip 7a extending from the inner lip 9a for sliding contact with an outer wall 6 of the groove 5 of the inner race. The center lip 7a is thin and highly resilient.
Another seal is disclosed in Japanese laid-open utility model publication No. 199534/87. As shown in FIG. 7, a resilient seal 1b extends from a seal groove of an outer race (not shown) into a groove 5 of an inner race and has a thin base portion R. A first lip 9b extends axial inwardly and then radially inwardly from the base portion R of the seal and terminates at the inner wall 8 of the groove 5. A second seal lip 7b has an L shape and extends axially outwardly to face the outer wall 6 of the circumferential groove 5 of the inner race leaving a labyrinth clearance therebetween.
The prior art seal 1a of FIG. 6 may accommodate axial displacement of the outer and inner races which may result when the outer race is rotated at a high speed and provide the desired seal integrity. However, in order to secure high seal integrity at high speed and high temperature, means must be provided to reduce the tolerances of associated parts (accuracy in shape and size of a seal and position of grooves in inner and outer races). This results in an increase in production cost. Since centrifugal force is increased in proportion to the square of the rotation speed of the outer race, grease moves strenuously and is vaporized when the rotational speed of the outer race increases. The grease in vapor form tends to be scattered externally of the bearing. Additionally, the air around the outer surface of the seal is agitated in response to the rotation of the outer race. This causes entry of foreign matter into the bearing. To this end, the labyrinth should be narrower when the outer race is rotated at high speed. In the first mentioned prior art seal 1a, the inner lip 9a is generally thick. As a result, centrifugal force is hardly applied to the inner lip, and the labyrinth clearance can not be reduced. The prior art seal 1a is not satisfactory at high speeds. In the second mentioned prior art seal 1b, although the base portion R of the seal lips is so thin that all the lips are moved together upon application of a centrifugal force since the inner lip 9b always contacts the inner wall 8, the labyrinth clearance t cannot be reduced sufficiently. Thus, desired seal integrity can not be achieved as such.